This invention relates to an optical pickup device and an optical disk device.
As an example of background art in the technical field of the invention, JP-A-2006-344344 is cited here. This patent document is described to seek to “retrieve a desired signal with high precision from an optical disk having a plurality of recording layers”. Another example is JP-A-2006-344380. This patent document is described to seek to “detect a tracking error signal with little offset even when an optical storage medium having two information recording planes is used. Further, in Technical Report CPM2005-149 (2005-10) published by The Institute of Electronics, Information and Communication Engineers, it is described that “a tracking photodetector is placed in an area free of stray light from other layers”. Its construction is disclosed also in JP-A-2004-281026.
Still another example of background art is JP-A-2008-102998. In this patent document it is described that “individual areas of a beam divider and a light receiving part of an optical detector are arranged so that when a target information recording layer on an optical disk is placed in focus, a light beam reflected from the target information recording layer focuses on the light receiving part of the optical detector and light beams reflected from other information recording layers are not thrown onto the light receiving part of the optical detector.”